/*
 * Radiotap parser
 *
 * Copyright 2007		Andy Green <andy@warmcat.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Alternatively, this software may be distributed under the terms of BSD
 * license.
 *
 * See README and COPYING for more details.
 *
 *
 * Modified for userspace by Johannes Berg <johannes@sipsolutions.net>
 * I only modified some things on top to ease syncing should bugs be found.
 */

#include "includes.h"

#include "common.h"
#include "radiotap_iter.h"

#define le16_to_cpu		le_to_host16
#define le32_to_cpu		le_to_host32
#define __le32			uint32_t
#define ulong			unsigned long
#define unlikely(cond)		(cond)
#define get_unaligned(p)					\
    ({								\
     struct packed_dummy_struct {				\
     typeof(*(p)) __val;				\
     } __attribute__((packed)) *__ptr = (void *) (p);	\
     \
     __ptr->__val;						\
     })

/* function prototypes and related defs are in radiotap_iter.h */

/**
 * ieee80211_radiotap_iterator_init - radiotap parser iterator initialization
 * @iterator: radiotap_iterator to initialize
 * @radiotap_header: radiotap header to parse
 * @max_length: total length we can parse into (eg, whole packet length)
 *
 * Returns: 0 or a negative error code if there is a problem.
 *
 * This function initializes an opaque iterator struct which can then
 * be passed to ieee80211_radiotap_iterator_next() to visit every radiotap
 * argument which is present in the header.  It knows about extended
 * present headers and handles them.
 *
 * How to use:
 * call __ieee80211_radiotap_iterator_init() to init a semi-opaque iterator
 * struct ieee80211_radiotap_iterator (no need to init the struct beforehand)
 * checking for a good 0 return code.  Then loop calling
 * __ieee80211_radiotap_iterator_next()... it returns either 0,
 * -ENOENT if there are no more args to parse, or -EINVAL if there is a problem.
 * The iterator's @this_arg member points to the start of the argument
 * associated with the current argument index that is present, which can be
 * found in the iterator's @this_arg_index member.  This arg index corresponds
 * to the IEEE80211_RADIOTAP_... defines.
 *
 * Radiotap header length:
 * You can find the CPU-endian total radiotap header length in
 * iterator->max_length after executing ieee80211_radiotap_iterator_init()
 * successfully.
 *
 * Alignment Gotcha:
 * You must take care when dereferencing iterator.this_arg
 * for multibyte types... the pointer is not aligned.  Use
 * get_unaligned((type *)iterator.this_arg) to dereference
 * iterator.this_arg for type "type" safely on all arches.
 *
 * Example code:
 * See Documentation/networking/radiotap-headers.txt
 */

int ieee80211_radiotap_iterator_init(
        struct ieee80211_radiotap_iterator *iterator,
        struct ieee80211_radiotap_header *radiotap_header,
        int max_length)
{
    /* Linux only supports version 0 radiotap format */
    if (radiotap_header->it_version)
        return -EINVAL;

    /* sanity check for allowed length and radiotap length field */
    if (max_length < le16_to_cpu(get_unaligned(&radiotap_header->it_len)))
        return -EINVAL;

    iterator->rtheader = radiotap_header;
    iterator->max_length = le16_to_cpu(get_unaligned(
                &radiotap_header->it_len));
    iterator->arg_index = 0;
    iterator->bitmap_shifter = le32_to_cpu(get_unaligned(
                &radiotap_header->it_present));
    iterator->arg = (u8 *)radiotap_header + sizeof(*radiotap_header);
    iterator->this_arg = NULL;

    /* find payload start allowing for extended bitmap(s) */

    if (unlikely(iterator->bitmap_shifter & (1<<IEEE80211_RADIOTAP_EXT))) {
        while (le32_to_cpu(get_unaligned((__le32 *)iterator->arg)) &
                (1<<IEEE80211_RADIOTAP_EXT)) {
            iterator->arg += sizeof(u32);

            /*
             * check for insanity where the present bitmaps
             * keep claiming to extend up to or even beyond the
             * stated radiotap header length
             */

            if (((ulong)iterator->arg - (ulong)iterator->rtheader)
                    > (ulong)iterator->max_length)
                return -EINVAL;
        }

        iterator->arg += sizeof(u32);

        /*
         * no need to check again for blowing past stated radiotap
         * header length, because ieee80211_radiotap_iterator_next
         * checks it before it is dereferenced
         */
    }

    /* we are all initialized happily */

    return 0;
}


/**
 * ieee80211_radiotap_iterator_next - return next radiotap parser iterator arg
 * @iterator: radiotap_iterator to move to next arg (if any)
 *
 * Returns: 0 if there is an argument to handle,
 * -ENOENT if there are no more args or -EINVAL
 * if there is something else wrong.
 *
 * This function provides the next radiotap arg index (IEEE80211_RADIOTAP_*)
 * in @this_arg_index and sets @this_arg to point to the
 * payload for the field.  It takes care of alignment handling and extended
 * present fields.  @this_arg can be changed by the caller (eg,
 * incremented to move inside a compound argument like
 * IEEE80211_RADIOTAP_CHANNEL).  The args pointed to are in
 * little-endian format whatever the endianess of your CPU.
 *
 * Alignment Gotcha:
 * You must take care when dereferencing iterator.this_arg
 * for multibyte types... the pointer is not aligned.  Use
 * get_unaligned((type *)iterator.this_arg) to dereference
 * iterator.this_arg for type "type" safely on all arches.
 */

int ieee80211_radiotap_iterator_next(
        struct ieee80211_radiotap_iterator *iterator)
{

    /*
     * small length lookup table for all radiotap types we heard of
     * starting from b0 in the bitmap, so we can walk the payload
     * area of the radiotap header
     *
     * There is a requirement to pad args, so that args
     * of a given length must begin at a boundary of that length
     * -- but note that compound args are allowed (eg, 2 x u16
     * for IEEE80211_RADIOTAP_CHANNEL) so total arg length is not
     * a reliable indicator of alignment requirement.
     *
     * upper nybble: content alignment for arg
     * lower nybble: content length for arg
     */

    static const u8 rt_sizes[] = {
        [IEEE80211_RADIOTAP_TSFT] = 0x88,
        [IEEE80211_RADIOTAP_FLAGS] = 0x11,
        [IEEE80211_RADIOTAP_RATE] = 0x11,
        [IEEE80211_RADIOTAP_CHANNEL] = 0x24,
        [IEEE80211_RADIOTAP_FHSS] = 0x22,
        [IEEE80211_RADIOTAP_DBM_ANTSIGNAL] = 0x11,
        [IEEE80211_RADIOTAP_DBM_ANTNOISE] = 0x11,
        [IEEE80211_RADIOTAP_LOCK_QUALITY] = 0x22,
        [IEEE80211_RADIOTAP_TX_ATTENUATION] = 0x22,
        [IEEE80211_RADIOTAP_DB_TX_ATTENUATION] = 0x22,
        [IEEE80211_RADIOTAP_DBM_TX_POWER] = 0x11,
        [IEEE80211_RADIOTAP_ANTENNA] = 0x11,
        [IEEE80211_RADIOTAP_DB_ANTSIGNAL] = 0x11,
        [IEEE80211_RADIOTAP_DB_ANTNOISE] = 0x11,
        [IEEE80211_RADIOTAP_RX_FLAGS] = 0x22,
        [IEEE80211_RADIOTAP_TX_FLAGS] = 0x22,
        [IEEE80211_RADIOTAP_RTS_RETRIES] = 0x11,
        [IEEE80211_RADIOTAP_DATA_RETRIES] = 0x11,
        /*
         * add more here as they are defined in
         * include/net/ieee80211_radiotap.h
         */
    };

    /*
     * for every radiotap entry we can at
     * least skip (by knowing the length)...
     */

    while (iterator->arg_index < (int) sizeof(rt_sizes)) {
        int hit = 0;
        int pad;

        if (!(iterator->bitmap_shifter & 1))
            goto next_entry; /* arg not present */

        /*
         * arg is present, account for alignment padding
         *  8-bit args can be at any alignment
         * 16-bit args must start on 16-bit boundary
         * 32-bit args must start on 32-bit boundary
         * 64-bit args must start on 64-bit boundary
         *
         * note that total arg size can differ from alignment of
         * elements inside arg, so we use upper nybble of length
         * table to base alignment on
         *
         * also note: these alignments are ** relative to the
         * start of the radiotap header **.  There is no guarantee
         * that the radiotap header itself is aligned on any
         * kind of boundary.
         *
         * the above is why get_unaligned() is used to dereference
         * multibyte elements from the radiotap area
         */

        pad = (((ulong)iterator->arg) -
                ((ulong)iterator->rtheader)) &
            ((rt_sizes[iterator->arg_index] >> 4) - 1);

        if (pad)
            iterator->arg +=
                (rt_sizes[iterator->arg_index] >> 4) - pad;

        /*
         * this is what we will return to user, but we need to
         * move on first so next call has something fresh to test
         */
        iterator->this_arg_index = iterator->arg_index;
        iterator->this_arg = iterator->arg;
        hit = 1;

        /* internally move on the size of this arg */
        iterator->arg += rt_sizes[iterator->arg_index] & 0x0f;

        /*
         * check for insanity where we are given a bitmap that
         * claims to have more arg content than the length of the
         * radiotap section.  We will normally end up equalling this
         * max_length on the last arg, never exceeding it.
         */

        if (((ulong)iterator->arg - (ulong)iterator->rtheader) >
                (ulong) iterator->max_length)
            return -EINVAL;

next_entry:
        iterator->arg_index++;
        if (unlikely((iterator->arg_index & 31) == 0)) {
            /* completed current u32 bitmap */
            if (iterator->bitmap_shifter & 1) {
                /* b31 was set, there is more */
                /* move to next u32 bitmap */
                iterator->bitmap_shifter = le32_to_cpu(
                        get_unaligned(iterator->next_bitmap));
                iterator->next_bitmap++;
            } else
                /* no more bitmaps: end */
                iterator->arg_index = sizeof(rt_sizes);
        } else /* just try the next bit */
            iterator->bitmap_shifter >>= 1;

        /* if we found a valid arg earlier, return it now */
        if (hit)
            return 0;
    }

    /* we don't know how to handle any more args, we're done */
    return -ENOENT;
}
